Breaking electronic point symmetries with light

Speaker: 
Anshul Kogar
Institution: 
UCLA
Date: 
Monday, June 3, 2024
Time: 
3:00 pm
Location: 
FRH 4135

Abstract: For centuries, we have known that when light propagates through a transparent solid, it can disperse, refract and exhibit nonlinear optical effects. However, until relatively recently, it has been more challenging to experimentally address the corresponding question: what happens to the transparent solid as light propagates through it? In this talk, I will outline processes by which the electronic degree of freedom can be driven far from equilibrium with the oscillating electric field of light and show the kinds of effects  that can be observed when matter is optically driven. I will share data from our group on Cr2O3, where inversion symmetry is broken by the antiferromagnetic order in the crystal, but the combined PT (parity, time reversal) symmetry is preserved. When linearly polarized light is transmitted through this system, the crystal exhibits a rotational symmetry breaking via optical rectification. Using interferometric time-resolved second harmonic generation, I show evidence that the broken symmetry state occurs only in the electronic subsystem, leaving the spins and lattice largely unperturbed. The axis of rotational symmetry breaking can be controlled with the polarization of the incident light. Our results build on previous work showing that macroscopic electronic effects in crystals can be induced through an optical drive, paving the way towards isolating the electronic contribution to the ferroelectric and magnetoelectric effect in crystals.

Host: 
Javier Sanchez-Yamagishi